I would look closely at the floor and the condition of the bottom of the WJ Pumped (Charger?) boat.
If the floor and stringers are solid, and the bottom is free of hook or rocker, It should handle a ~500 HP big block.
My old Glenco, with 1/4 'engine' stringers, ran 72 gps'd with a WJ pump, no ride plate, shoe, loader, just a Place Diverter, spinning a jacuzzi 'b' at ~5200 r's.
The YJ can be outfitted with Berk style bowl and impeller...$$$
Dan'l